CC2520: CC2520

In IEEE 802.15.4 every 4-bit symbol is encoded into a sequence of 32 chips that are actually transmitted over the air. The 32 chips
as a whole is also called a pseudo-noise code (PN-Code).

I found the following doing a google search, showing a table with the Symbol to Chip Mapping

www.kaishunwu.com/uploads/soft/150201/chiperror.pdf

Thank you but my main question is about the encoding process , is it multiplication like in conventional DSSS or just replacement of the 4 bits by the assigned codeword?

In the document I reffered to it says: "In IEEE 802.15.4, a 4-bit data symbol is mapped to a 32-chip PN-Code as shown in Table 1."

Table 1 shows all possible 4-bits symbols and their corresponding 32-chip PN-Code.

It is my understanding that NO multiplication is done, you simply replace the 4 bits with the corresponding 32 chips.

Thank you again

That would mean that no code modulation is done by the symbol(4 bits) so how is this symbol going to be recovered at the receiver end? A look up table cannot recover a stream of data at a certain rate. 

Moreover I looked at one example in Matlab for 802.15.4

EVM Measurements for a 802.15.4 (ZigBee®) System

The code shows the following:

  % Convert symbols to chips (spread)
    c = reshape(chipValues*x', simNumSymbols, 1);
chipValues is the code sequence and x is the symbol (4 bits) and that is a multiplication. So I am still a bit puzzled as I do not know of any DSSS that does not modulate (multiply) the code sequence with the data. I am sorry if I keep asking but I would very much appreciate it if you could again check that
Thank you for your help, effort and assistance

 

.

   

I am sorry but I do not know all the details on how things are done internally on the chips. All I know is that when you transmit with DSSS, it does DSSS encode the data, and when you receive, it is encoded. Everything according to the spec.

I have no more info on this and will mark the case as solved from our end, but other people can still post answer if they have something information to add.

Siri

Thank you for your reply. May I ask you to check on your end how is encoding of the data  being done .  This is really an important matter for me and for my company. This could really be a pure theoretical question but then it is important sometimes to align theory with practice

Thank you

Hatem

Sorry to bother uou again. Are there other people at TI that I can ask about this issue. Perhaps people that are more oriented towards the theory of DSSS?

Normally we don't share details about how the modem does the encoding. Why is it important to know the details?

Closing this thread do to inactivity.

The answer provided by TI did not resolve the issue. It certainly requires someone well informed and knowledgeable on the topic of Direct Sequence Spread Spectrum

My last response was
"Normally we don't share details about how the modem does the encoding. Why is it important to know the details?" I have not gotten a response on why you need this detailed information even though you state that it's very important for your project.

Nothing really proprietary here... all I need is someone who knows about the 802.15.4 standard and knows the theory of spread spectrum to answer this question

As said, we don't share what we do internally on the chip. General theory can be found in the literature.